1. Field of the Invention
The present invention relates to a motion estimation method and device adaptive to change in illumination, more particularly to a method and device that can efficiently encode and decode an image by use of a motion estimation (ME) process and a motion compensation (MC) process adaptive to change in illumination.
2. Description of Related Art
ITU-T and ISO/IEC developed the H.26x series and MPEG-x series while studying to improve efficiency in image encoding. H.264 (part 10 Advanced Video Coding, MPEG-4) was completed in 2003 and thus many bits could be saved. Studies for block matching motion estimation (BMME) were vigorously carried out with development of such video coding standards. In most methods, the sum of absolute differences (SAD) (hereinafter, referred to as “SAD”) between blocks of the current frame and candidate blocks of the reference frame is calculated, and the position of the candidate block of the reference frame corresponding to the least SAD is determined as a motion vector of the blocks of the current frame.
Then, discrete cosine transform (DCT) and quantization are performed to difference signals (residual) between the candidate block and the current frame block, and variable length coding (VLC) is performed like the motion vector. Here, since the search for the motion vector means that the motion vector is acquired by removing temporal redundancy between the current frame and the reference frame, the encoding efficiency is remarkably improved, but there are the following problems:
When illumination changes (e.g., scene change in an image, fade-up or fade-down, or flickering) between inter-views input through different cameras at the same time axis or between same-views input through the same camera at continuous time axes at the time of multi-view video coding, calculating SADs between blocks, using the conventional art, to obtain the least SAD and encode a difference signal takes an excessive quantity of bits, drastically slowing the compression ratio.
Generally, when there is a scene change, intra encoding is more effective than the motion estimation and the motion compensation for the changed frame. This is because the pattern of the current frame block cannot be found in any search area of the reference frame. Similarly, when there is flickering or a change in lighting, similar results are obtained by use of the same method of encoding the difference signal through the motion estimation. Hence, it is often intra encoded. However, in this case, since there was no scene change, a block having a pattern similar to the current frame block can be found from the reference frame, but it takes a large volume of bits for encoding the difference between the block and the current frame block.